1. FIELD OF THE INVENTION
This invention relates to a novel filter media and its uses; more particularly, this invention relates to a filter media useful for oxidizing and removing soluble iron and manganese and/or removing and inactivating microorganisms from fluids, particularly aqueous fluids.
2. PRIOR ART
Soluble iron, usually as a solution of ferrous bicarbonate, is a common contaminant in water supplies, particularly well water. Soluble iron in excess of 0.3 parts per million can cause undesirable taste and odor, discoloration of washed clothes, discoloration of plumbing fixtures, incrustation in water systems, discoloration of manufactured products such as textiles or paper, and other problems. These problems generally arise when the water contacts air, chlorine, and/or other chemicals capable of oxidizing the soluble ferrous ion (Fe++) to the less soluble ferric state (Fe+++). Hydrous ferric oxide, i.e. ferric hydroxide, is formed which is essentially insoluble in water and is thus precipitated in the water by the oxidation reaction. This is the familiar red-brownish, or rusty appearance on sinks, swimming pools, clothing and the like.
Along with the soluble iron contaminants, a water supply may also contain insoluble iron, as well as dissolved manganese and other undesirable soluble contaminants, e.g. copper, chromium, and hydrogen sulfide. All of these soluble contaminants may also be present in their colloidal form.
It has been the practice in the past to utilize an oxidizing agent for the purpose of oxidizing the soluble iron (and other contaminants) to a condition in which they can be precipitated and subsequently removed from the water. Among such oxidizing agents are the various permanganates, such as those of potassium or calcium, hypochlorides and chlorine. Such oxidizing agents will oxidize, for example, soluble iron, however, such agents introduce objectionable residues into the water and/or are inconvenient for use, particularly, for example, in a residential environment. Thus, for example, the permanganates introduce soluble manganese salts into water, while chlorine and the hypochlorides introduce objectionable tastes and odor. Such residues are difficult to remove and for this reason the use of such oxidizing agents for the purification of water has been distinctly limited. Furthermore, it has been recently discovered, that chloroform, which may be produced through the chlorination of water, is a carcinogen. The potential for introducing such a residue into a water system makes the chlorination of water a less desirable means for oxidizing contaminants such as soluble iron. The use of oxidizing agents which do not introduce objectionable residues into the water, such as hydrogen peroxide, are inconvenient to use, particularly in a residential environment.
For example, the chlorination of water followed by filtration has been commercially used for the removal of both soluble and insoluble iron. Chlorine, for example in the form of sodium hypochloride, is injected into the water contaminated with iron. The iron is oxidized and allowed to precipitate and flocculate to a size large enough for removal by subsequent filtration. The shortcomings of this system, in addition to the aforementioned, are (1) three pieces of equipment are required, i.e. a metering pump, a holding tank and a filter; and (2) a 30 minute retention time is generally required for flocculation--this would require a holding tank of about 300 gallons if flows of 3 gpm are required. Such a system would be particularly undesirable in a residential environment.
Aeration of water followed by filtration has been an extensively used method for reducing the quantity of metallic impurities present in water, but even under the most effective conditions, aeration will remove only from 80 to 90 percent of the soluble iron. Again such a procedure is completely unacceptable for use in a residential environment and requires at least two separate process steps as well as a retention time for flocculation.
Other attempts at removing soluble iron have involved, for example, the use of ion exchange beds, i.e. water softening. Such a method is perhaps one of the most widely used methods for iron removal. The method, however, is only recommended for the removal of soluble iron. The process requires charging an ion exchange material, such as sulfonated polystyrene resins, with sodium ions (Na+), preferably using sodium chloride (salt). As the soluble iron contaminated water is passed thru the resin bed the iron ions are exchanged for sodium ions which are released into the water. The short-comings of this system are that the resin also exchanges other multivalent positive ions in the water for sodium ions. This greatly reduces the life of the resin and produces an unnatural water supply wherein all the positive ions are sodium. This can present a health hazard to people on low sodium diets. Also, the backwash from the regeneration process may present problems to sewers and septic systems and contaminate surface and ground waters with salt. The contaminated water may also require pretreatment with sequestering or chelating agents, e.g. polyphosphates, to prevent the precipitation of iron onto the resin. Thus ion exchange methods for the removal of iron are expensive, inefficient and generally not suitable for use in a residential environment.
Another commercial process for removing soluble and insoluble iron from water is the "greensand filter" method. Generally, the process requires charging manganese greensand (i.e. modified New Jersey Gluconite sand) with potassium parmanganate. As the iron contaminated water is passed thru this greensand bed the soluble iron is oxidized by the permanganate to the insoluble form and filtered through the deep bed. The short-comings of this process are (1) the system has a very low capacity and short life requiring frequent backwashing and regeneration--this may present problems to sewers and septic systems and contaminate surface and ground waters; (2) the oxidation, flocculation and filtration reaction time for soluble iron is long, requiring a bed depth of at least 24 inches; and (3) the potassium permanganate used for regeneration is hazardous and inconvenient to use.
Another similar method of removing iron from water, which has only limited application, involves passing the contaminated water through a granular bed of partially calcined dolomitic lime--calcium magnesium carbonate. However, even with the use of filter aid, it is sometimes difficult and economically impossible to reduce the amount of iron in water supplies to an acceptable level.
Thus it can be seen that the aforementioned methods for removing soluble iron from water may require at least two process steps, i.e. pretreatment with an oxidizing agent followed by removal of the oxidized iron, long reaction times and complicated and expensive process equipment.
Additionally, such devices can experience long periods of non-use which can result in the build up of microorganism populations. Subsequent process steps and equipment can be used to remove such microorganisms, making the system even more complicated and expensive.
The destruction of microorganisms, e.g. rickettsiae, bacterium, protista, virus, through the application of filtration or chemical compounds is known. For example, it has long been recognized that low concentrations of silver ions or silver bearing materials that yield silver ions will combine with the sulfhydryl groups in bacteria and other microorganisms to form stable silver-sulfur complexes within the cell. Such complexes block oxidative reactions and hydrogen transfer within the cell resulting in the eventual death of the cell. Practical application of this knowledge to potable water is seriously limited by the fact that excessive concentrations of silver may be harmful to humans and to domestic animals and by the physical difficulty of maintaining an effective and safe concentration of active silver in water.
The destruction of microorganisms through the application of oxidizing substances, such as chlorine, oxygen and ozone has long been the practice for disinfecting drinking water, swimming pool water and the treatment of sewerage. However, conventional oxidizers are subject to a number of disadvantages. For example, both chlorine and ozone must be fed continuously into the water and in time both lose their oxidizing power. Furthermore, as indicated, previously, it has been discovered that chloroform produced through the chlorination of water, is a carcinogen. Chlorination has thus become a less desirable form of disinfecting potable water. As an alternative to chlorine the use of ozone (O.sub.3) has recently come into prominence. While ozone is a very effective oxidizing agent, it is chemically unstable and must be generated continuously at the point of application. The generation of ozone requires a corona discharge of high voltage electricity. The use of ozone for the treatment of water supplies thus becomes uneconomical and impractical, particularly in a residential environment.
The use of filters to mechanically remove microorganisms such as bacteria, is known. Such filters exhibit a short life due to pore blockage and exceedingly low rates of filtration due to the small pores required to filter such microorganisms. Attempts to minimize these problems by charge modifying the filter media through various means to enhance the capture potential of the filter media, have met with various degrees of success--see, for example: U.S. Pat. Nos. 4,007,113 and 4,007,114 to Ostreicher; copending U.S. Ser. No. 164,797, filed on June 30, 1980, and 147,975, filed on May 8, 1980 and 123,467, filed Feb. 21, 1980, all to Ostreicher et al; U.S. Ser. No. 201,366 filed Nov. 27, 1980 to Emond et al; and ZETA-PLUS.sup.(R) and ZETAPOR.sup.(TM) filter media sold by AMF Cuno, Meriden, Connecticut. Such filter media, however, tend to be too expensive and impractical for a residential environment.
More specifically, methods of removing iron from water are described in the following U.S. Pat. Nos.:
1,253,840 to Kobelt; PA0 2,237,882 to Lawlor et al; PA0 2,311,314 to Reichert et al; PA0 3,102,789 to Pirsh et al; PA0 3,167,506 to Fackler et al; PA0 3,192,156 to Joyce; PA0 3,222,277 to Joyce; PA0 3,235,489 to Bell et al; PA0 3,259,571 to Marshall et al, and PA0 3,399,136 to Bell. PA0 850,608 to Schroeder; PA0 975,405 to Eilertsen; PA0 1,082,315 to Gans PA0 1,473,331 to Bechhold; PA0 1,557,235 to Bechhold; PA0 1,734,197 to Blumenburg; PA0 2,008,131 to Dieck et al; PA0 2,066,710 to Bado; PA0 3,248,281 to Goodenough; PA0 3,268,444 to Reun; PA0 3,872,013 to Nishino et al; and PA0 4,071,636 to Nishino et al. PA0 (a) magnesium peroxide (MgO.sub.2) or PA0 (b) calcium peroxide (CaO.sub.2).
Methods of inactivating and removing microorganisms from fluids are described in the following U.S. Pat. Nos.:
Kobelt describes a process for removing manganese and iron from water which requires adding to the water soluble permanganate and subsequently filtering the water through an " . . . extremely intensely acting . . . " catalytic body of high porosity. The catalytic body is mixed with a material capable of generating oxygen when reacted with the water. Materials capable of generating oxygen are said to be peroxides of metals insoluble in water. It is stated that these peroxides when present in the catalytic body accelerate and complete the conversion of the iron and manganese existing in the water into oxide and hydrates insoluble water so that they may be completely separated by the catalytic body. The catalytic bodies that may be used are said to be trachytes or their tuffs, and similar volcanic rocks. A volcanic scoria or gravel having mud deposited thereon may also be used.
Fackler et al, describes a process for the removal of iron and manganese, similar to a "greensand filter" but which requires adding permanganate to the water as it is being fed to a manganese oxide zeolite filter bed. The filter medium described for removing the oxidizables from the water may contain a large proportion of the higher oxides of manganese, i.e. an oxidation number of about 4.
Both Joyce references describe percolating a hydrogen sulfide containing water through a bed of activated carbon which is impregnated with manganese dioxide. Hydrogen sulfide is removed from the water. The water is then passed through a cation exchange water softener to remove the water soluble manganese and iron compounds. It is said to be critical that the activated carbon be impregnated with manganese dioxide and not merely coated therewith. It is therefore necessary to form the manganese in situ, e.g., passing an aqueous solution of an alkaline metal permanganate through the activated carbon.
Marshall et al, describes a process for removing soluble iron from water which requires adding powdered active magnesium oxide and pulverulent filter aid to water, mixing for a period of time, " . . . up to say 10 minutes . . . " and then passing the mixture through a filter. The filter aids are described as diatomaceous silica, perlite, siliceous material, carbon and fiber matter, such as asbestos and cellulose. The magnesium oxide may be in the form of calcined magnesite or partially calcined dolomite.
Gans, describes the sterilization of water by filtration over oxides of manganese in conjunction with zeolites, or after the addition of excess permanganates, filtration over reduced oxides of manganese in conjunction with zeolites. Gans purifies water by producing in the water a colloidal solution of manganese and subsequently filtering it over an oxide of manganese. The colloidal solution of manganese is produced by the addition of permanganates to the water.
Dieck et al, describes sterilization of liquids by contacting the liquid with a silver oxide compound and manganese oxide. It is contemplated by Dieck et al that this composition may be embedded in a finely divided form in or upon porous substances such as filter candles. The filter materials can be produced by adding the pulverulent composition to a porous substance and then forming filter plates.
Bell, describes purifying water contaminated with bacteria and virus by adding iron or aluminum to the water to combine with the bacteria and viruses. The iron or aluminum is then removed by adding a filter aid and a compound such as magnesium oxide which will unite with the iron or aluminum iron to form a substance which can subsequently be removed by filtration.
As can be seen from the foregoing, most of the methods for effectively oxidizing and removing soluble iron and/or effectively removing and inactivating microorganisms cannot be accomplished with a single process step or filter media. All of the aforementioned methods require numerous process steps, e.g. pretreatment, retention time, filtration, etc., to be completely effective. All of these are therefore comparatively expensive and complicated, and in particular are impractical in a residential environment, where simplicity and cost are key factors.